Impossibility to mount a Sinatra app

It's currently impossible to mount any Sinatra application on
rails3.
The route is recognized by the rake routes command.
But whenever we go to it in the browser or we execute it in the
tests, we get a ActionController::RoutingError exception.

I've written a test case that reproduces it (but as I didn't
succeed to reproduce it without Sinatra, it includes the framework.
So it's not committable to rails).http://gist.github.com/376653

So I guess that's not really a bug but an improvement.
In Rizwan's example, the Sinatra app is mounted in the "/sinatra"
directory. And it does gets on /.
This requires any Sinatra mounted application to be aware of the
directory in which it'll be mounted. And if we change this
directory, we need to also change all the routes in the sinatra
app.

Moreover, it forbids us to mount external apps without updating
them.
For example if I wanted to mount the resque's web app in the
"/resque" directory, I couldn't without updating the sinatra app in
the gem.